The HD-Zip I transcription factor ATHB5 regulates source-to-sink transport of sucrose in Arabidopsis thaliana

RAMINGER, BETINA LORENA; CABELLO, JULIETA VIRGINIA; ZAPATA, CARLOS; MIGUEL, VIRGINIA NATALÍ; CHAN, RAQUEL LÍA

Santa Fe

Congreso; XXXIII Argentinian meeting of Plant Physiology; 2021

Sociedad Argentina de Fisiología Vegetal

AtHB5 is a HD-Zip I transcription factor from Arabidopsis thaliana. It was previously reported that during stem maturation AtHB5 expression decreased and it was the only HD-Zip I that exhibited this behavior. To investigate its biological function, two strategies were carried out: AtHB5 expression patterns were studied and mutants and overexpressing lines (OE) were obtained. Arabidopsis plants transformed with AtHB5 promoter fused to GUS reporter gene indicated expression in hypocotyl and vascular tissue.A phenotypic analysis showed that athb5 plants had wider and more lignified stems, while OE had narrow and less lignified stems than WT. Furthermore, athb5 stems exhibit more phloem and xylem vessels than WT as well as in vascular tissue from leaves and pedicel. Also, OE had more starch on rosette leaves than WT and had modified expression levels of several enzymes involved in starch synthesis and degradation pathways. Moreover, aniline blue staining showed that OE had more callose in rosette leaves than WT, indicating a defective sugar transport. Regarding to root system, under normal conditions athb5 had larger roots while OE had shorter roots than WT. Furthermore, under complete dark conditions there were no differences between genotypes, but when they were supplemented with sucrose, athb5 exhibited larger roots than WT and OE shorter. Altogether these results suggest that AtHB5 regulates negatively source-to-sink transport of sugar in Arabidopsis.